In recent years, a teletext of coding transmission system has come into practical use that allows character and graphic information such as news, weather forecasts, and stock market, which are provided by combinations of characters and graphics, to be presented on a screen of a household television receiver. Also, there have been developed television receivers with a built-in receiver for receiving teletext in a coding transmission system. Hereinbelow, the teletext and its teletext receiver equipment in a coding transmission system as described above are explained with reference to the drawings.
FIG. 1 shows a construction of a conventional teletext receiver. In the figure, represented by reference character a is a television video signal; so by numeral 1 is a character signal extracting section for extracting character signals superimposed on the vertical blanking intervals from the video signal a; 2 is a data block linking section for linking the character signals in the units of data blocks extracted by the character signal extracting section 1 and classifying them into data groups; 3 is a data type deciding section for deciding whether the data groups classified by the data block linking section 2 are program data, page data, or index data; 4 is a character-program data decoder section for decoding character-program data according to the types of data decided by the data type deciding section 3 to develop the data into characters and graphics for display; 5 is a buffer memory section for accumulating the signals decided as character-program data by the data type deciding section 3; 6 is a display control section for actually displaying display data developed into characters and graphics at the character-program data decoder section 4 on a screen or the like; 7 is a video memory section for storing display data to be actually displayed on the screen or the like by the display control section 6; and 8 is a sound generator section for performing actual sound generation according to added sound data decoded by the character-program data decoder section 4.
FIG. 2 shows the hierarchy of a teletext signal of the coding transmission system. In the FIG. 2, hierarchy 1 is a physical layer, representing the item elements of a character signal as an electrophysical signal. This signal is also superimposed on 14H, 15H, 16H, and 21H of the vertical blanking interval of the television signal. At a link layer of a hierarchy 2, the character signal is treated as logical data of either 1 or 0. Data lines, each of which refers to a transmission unit of character signals transmitted during one horizontal scanning line interval of a television video signal, is composed of a synchronization part and a data packet. The data packet, which refers to a part of the data line in which the synchronization part is eliminated, is composed of a prefix, data blocks, and check codes. Primarily the function of prefix is exerted at hierarchy 3 of a network layer. The prefix refers to data for identification and control, added to the head of the data packet, while the data blocks refer to a part of the data packet in which the prefix and the check code are eliminated, for transmitting various types of information data. Hierarchy 4 is a transport layer, representing the functions of data groups. The data groups are composed of data groups, each being one group of information data transmitted by one data block or a plurality of data blocks. Hierarchy 5 is a session layer, representing the structure of program data and functions for identification control of the program, and the like. Hierarchy 6 is a presentation layer, representing the functions of coding the presentation, where the coding for displaying characters and graphics and for presenting added sounds is specified.
FIG. 3 shows the structure of program management data and page data. Transmitted to the head of the program data is program management data pertaining to the whole of the program. The program management data or page data is composed of a data header and several units.
FIG. 4 shows the structure of a data group header and the transmission procedure thereof. Referring to FIG. 4, the data group header is composed of a data group identification code for identifying and controlling data groups, a data group retransmission code, a data group link code, a data group serial number, data group size, and working data. In this structure, the data group identification code represents the type of a data group by binary value, where program management data or page data is assigned "0", while program index data is assigned "15."
FIG. 5 shows the structure of a data header and the transmission procedure thereof. Referring to FIG. 5, the data header is composed of data-header identification, data-header data length, and data-header data. The data-header identification represents the function of identifying the type of a data header, and the coding representation thereof is composed of an information separation code and data-header parameters. Correspondence between data headers and parameters is such that program data header, page data header, program search data header, and continuation data header correspond to data-header parameters 02/0-3, respectively.
FIG. 6 shows the structure of a data unit and the transmission procedure thereof. Referring to FIG. 6, the data unit is composed of data-unit identification, data-unit data length, and unit data. The data-unit identification represents the function of identifying the type of a data unit, and the coding representation thereof is composed of a data-unit separation code and data-unit parameters. Data-unit parameters of the current system are assigned 16 types of identification parameters such as text, header text, a color map, and a program index. A data-unit link flag represents whether or not the succeeding data unit is a continuation data unit and to be linked, while the data-unit data length represents the data length of a data-unit data. The data-unit data is a piece of data that represents the number of data represented by data-unit data length.
FIG. 7 shows the assignment of the current data-unit parameters. In FIG. 7, the blank fields are unused.
FIG. 8 gives an example of coding in the current teletext. In FIG. 8, there are two data units, and data-unit parameters are "24H" and "20H," these two data units representing "header text" and "text," respectively.
The teletext receiver equipment constructed as in FIG. 1 is now described about its operation.
From the input video signal a, the character signal extracting section 1 extracts character signals superimposed on the vertical blanking intervals 14H, 15H, 16H, and 21H. The data block linking section 2 picks up data blocks out of the character signals extracted at the character signal extracting section 1, and thereafter links the data and classifies them into data groups. The data type deciding section 3 decides whether the data groups classified by the data block linking section 2 are program data, page data, or index data, according to data group identification codes. Thereafter, the character-program data decoder section 4 accumulates character-program data derived from the data type deciding section 3 in the buffer memory section 5, while it extracts character-program data pertaining to a program number needing presentation from the character-program data accumulated in the buffer memory section 5. According to the type of the character-program data, character signals are decoded as shown in FIG. 8, and the resulting character/graphic screen information is written into the video memory section 7 through the display control section 6. The display control section 6 sequentially reads the character/graphic screen information written into the video memory section 7, yielding an output of display signal b. Further, if the program data needing presentation has any added sound information, the character-program data decoder section 4 decodes the added sound information, and transmits sound-generation data to the sound generator section 8, where the sound generator section 8 produces a sound signal based on the sound-generation data.
In the teletext, data transmission is carried out in the above-described transmission procedure. On the side of teletext receiving equipment, character and graphic information coded according to the transmission procedure are decoded, offering the services that still images such as news and weather forecasts are displayed on television. More recently, with a view to making the teletext further widespread, new services are under discussion in which television-program table information (program title, program broadcasting date, program broadcasting time, etc.) are encoded, transmitted as data unit data by expanding the transmission procedure while compatibility with the conventional teletext is maintained (i.e. by defining new parameters), so as to allow the teletext to be utilized for video recording reservation by image recording/reproducing apparatus such as VTRs. However, the conventional teletext receiving equipment cannot afford such expansion of the transmission procedure as it stands, prohibiting their users from enjoying the new services.
Meanwhile, since the operation for recording reservation with the current VTRs is so complicated and difficult to understand that beginners and those unfamiliar to video/audio appliances cannot manage it. This accounts for the strong desire that this operation for recording reservation be made easier.
The present invention, in view of the foregoing problems, has developed a transmission system in which television-program table information is defined on transmission, and further provides a receiving apparatus in which the television-program table information is recognized and processed on the receiver side so that the recording reservation in the image recording/reproducing apparatus can be simplified and that change in the time of recording reserved programs can be treated.